Introducing a grain refining or alloying agent into molten metals and alloys

ABSTRACT

A molten metal or alloy is inoculated with metallic treating agent by pouring the molten metal into a troughlike passageway and by introducing a rodlike supply of the metallic treating agent into the molten metal flowing in the passageway under conditions insuring a disturbed but nonturbulent flow of the molten metal and resulting uniform distribution of the treating agent therein.

United States Patent Inventor Jean C. Hoff Stamford, Conn. Appl. No.791,453 Filed Jan. 15, 1969 Patented Jan. 11, 1972 Assignee KaweckiBerylco Industries, Inc.

New York, N.Y.

INTRODUCING A GRAIN REFINING OR ALLOYING AGENT INTO MOLTEN METALS ANDALLOYS 2 Claims, 1 Drawing Fig.

US. Cl 75/135, 75/138 Int. Cl C22c 1/06 Field of Search 75/l 35, 53,

[56] References Cited UNITED STATES PATENTS 2,595,292 5/1952 Reece75/122 3,331,680 7/1967 Leupold a 75/53 Primary Examiner L. DewayneRutledge Assistant Examiner-E. L. Weise AttarneyPennie, Edmonds, Morton,Taylor and Adams ABSTRACT: A molten metal or alloy is inoculated 'withmetallic treating agent by pouring the molten metal into a troughlikepassageway and by introducing a rodlike supply of the metallic treatingagent into the molten metal flowing in the passageway under conditionsinsuring a disturbed but nonturbulent flow of the molten metal andresulting uniform distribution of the treating agent therein.

PATENTED JAN] 1 1972 m Jean C. No"

INTRODUCING A GRAIN REFINENG R ALLOYING AGENT INTO MOLTEN METALS ANDALLOYS This invention relates to the modification of a molten metal oralloy with a master alloy of that metal containing a grain refining oralloying agent, or both.

The presently preferred method of introducing a grain refining agentinto a metal such as aluminum and its alloys comprises adding analuminum base master alloy containing the grain-refining agent to themolten aluminum or aluminum alloy in a holding furnace or casting ladle.The grain refining agent is an aluminum-insoluble metal, alloy orintermetallic compound which, when uniformly distributed throughout themolten aluminum, remains solid (or solidifies before the aluminum) andcauses the aluminum to crystallize in fine grain size when the lattersolidifies. In order to achieve this result, however, the grain-refiningagent, which is added in very small amounts compared to the molten hostmetal, must not only be well distributed initially throughout the moltenmetal but it must remain well distributed until the molten host metalsolidifies.

In order to obtain good initial distribution of a grain refining oralloying agent, there has been used heretofore an aluminum master alloycontaining the agent in uniform distribution throughout the aluminumbase. When this master alloy in solid form is added to a mass of themolten aluminum prior to casting, the solid metallic aluminum componentof the master alloy melts and liberates the grain refining or alloyingagent. In order to effect more uniform initial distribution of thetreating agent throughout the molten aluminum, the master alloyheretofore has been added as relatively small discrete masses, but thesmaller these discrete particles the more they contain combined oxygenfrom atmospheric oxidation and the larger the particles the more theytend to segregate in the bottom of the mass of molten aluminum.

Proposals have been made heretofore for introducing one metal into astream of another molten metal, but these proposals have eitherintentionally or inadvertently introduced the extraneous metal of suchcomposition, or in such a manner, as to cause disruption of the stream.In many casting operations, such turbulence as is evidenced bydisruption of the metal stream is considered intolerable or at leastundesirable because it promotes dissolution of the ambient at mosphere,or of one of its components, in the molten metal.

I have now devised a method of inoculating molten metals and alloys witha metallic treating agent such as a grain refining or alloying agentwhich avoids the problems experienced heretofore yet assures uniformdistribution of the treating agent or of one of its constituentsthroughout the metal to which it is added. The method of the inventioncomprises pouring the molten metal from a source thereof into a confinedtroughlike passageway to form a stream of the molten metal flowingthrough the passageway, and simultaneously feeding into the turbulentmass of molten metal flowing in the trough a flow-disturbing solidrodlike supply of the treating agent, the rodlike supply of the agentbeing introduced into the stream of molten metal in such manner as toeffect a significant disturbance of the flow without impairing theintegrity of the stream. The rod is supplied at a rate not in excess ofthat at which it is consumed in the flowing molten metal in the trough,and the resulting inoculated molten metal is discharged into a castingzone. By feeding the master alloy into the molten metal flowing in thetrough at a predetermined rate, the molten metal discharged to thecasting zone will contain a predetermined proportion of the treatingagent uniformly distributed therethrough.

The molten metals which can be treated by the method of the presentinvention include substantially pure metals and their alloys such, forexample, as aluminum, zinc, copper, iron, nickel, and the like, whichare to be cast.

The useful master alloys in practicing this invention are thosegenerally considered to be compatible with the molten metal to whichthey are added. The treating agent component of the master alloy can beany metal, alloy or intermetallic compound which, when added to themolten host metal or alloy, causes the molten metal to be modified asdesired. The grain refining and alloying agents generally usedheretofore for the aforementioned metals and alloys are useful inpracticing the present invention. These agents include boron, titanium,zirconium, niobium, tantalum and titanium, and zirconium, niobium, andtantalum borides and are contained in a metal base in amounts generallynot exceeding about 10 percent by weight. For example, representativealuminum-base master alloys of this type are 0.5 to 5 percent boron,balance aluminum; 2 to 10 percent titanium or zirconium, or total ofboth, balance aluminum; and 0.1 to 5 percent boron, 2 to l0 percenttitanium or zirconium, or total of both, balance aluminum. Similargrain-refining agents, except for their base metal, can be used forgrain refinement of metals other than aluminum, but additional agentssuch as master alloys containing manganese and iron can be used forcopper, brass and bronze. All of these treating agents are applicablefor steel and other nonferrous metals, not only for grain refinement butfor general alloying purposes. The composition of the master alloyshould, of course, be as uniform as possible in order to obtain themaximum benefit of the unifonn distribution of the grain-refining agentthroughout the molten host metal obtained by practice of the method ofthe present invention.

The added agent is supplied in the form of a solid rodlike body, thatis, either in the form of a rod, wire, bar or strip, formed by anyconventional procedure such as direct chill and continuous casting,extrusion, rolling, or rolling and drawing operation. The cross sectionof the rodlike body can be circular, oval, square, oblong, etc., butshould offer a substantial impediment to the flow of the molten metalstream so as to effect a significant disturbance in its flow. Ingeneral, these rodlike forms range advantageously from about one-eighthinch to about one-half inch in diameter or maximum cross section, butsmaller and larger sizes can be used effectively. The actual size isdetermined by the rate at which the master alloy is to be supplied tothe molten metal, a relatively small diameter rod or wire beingpreferred for any predetermined supply rate in order to offer a maximumsurface area: mass ratio for most efiicient consumption of the masteralloy in the flowing molten metal. The rods can be any convenient lengthsuch, for example, as SOO-foot sections wound on a reel. However, theindividual sections can also be welded end to end to obtain a virtuallyendless rod which is particularly desirable for supplying the treatingagent to a continuous casting operation.

Pursuant to the invention, the rodlike master alloy is fed directly intoa confined path of the molten metal flowing from a source thereof to acasting zone.

A trough is commonly used for carrying the molten metal from a holdingfurnace to a casting zone, and in such a case the rodlike master alloyis fed to the molten metal flowing through this trough. In operationswhere the trough delivers the molten metal to a distributor box fromwhich the molten metal is distributed to a number of casting molds, therodlike master alloy is advantageously introduced into the molten metalin the distributor box. Because of the problem of potential settling andresulting segregation of the treating agent or of one of its componentsin the molten metal in a casting mold, it is common practice to maintainthe temperature of the molten metal in the holding furnace or castingladle as close as practicable to the freezing point of the metal andthus limit the amount of superheat in the metal as it is cast.Consequently, it is presently preferred to introduce the master alloyrod or wire into the hottest zone of the turbulent molten metal stream,this generally being the zone closest to the point of delivery of themolten metal from the holding furnace or supply ladle. In addition tothe advantage of greater heat availability in this zone for melting thebase metal component of the master alloy, it has been found that thiszone frequently is the one characterized by the greatest degree ofcirculation and therefore the zone most conducive to consumption andthorough admixing of the master alloy in the molten metal. Thecirculation of the molten metal as it flows through the remainder of thetrough, or through branch troughs from a distributor box, as describedhereinbefore, further effects and maintains thorough and uniformdistribution of the treating agent in the molten metal as it isdischarged to the casting zone.

In order to promote disturbance of the flow of the molten metal so as toincrease its circulation in the trough without disruptive turbulence, ithas been found particularly advantageous to feed the rodlike treatingagent obliquely upstream into the stream of molten metal. As shown inthe single FIGURE of the accompanying drawing, the rod 1 is fed throughthe open top of the trough 2 and in a direction toward the source 3 ofthe stream 4. In this way, the relatively blunt cross section of the rodis presented to the flow of molten metal and causes a significantdisturbance in its flow pattern. The portion of the rodlike mass ofagent immersed in the mo]- ten metal immediately downstream of thisleading end tends, by surface tension between the molten metal and therod, to hold the flowing molten metal in contact with the rod for asubstantial distance downstream from the disturbance caused by itsleading end and thus counteracts any tendency for the disturbance tocause disruption of the integrity of the stream. The sidewalls of thetrough confine the flow of the stream beyond the point of addition ofthe agent and help to perpetuate throughout the length of the trough thedisturbed flow, and the resulting mixing, produced upstream pursuant tothe invention. Where the nature of the molten metal permits greater flowdisturbance, the rod of treating agent can be introduced at a rightangle into the stream, but in this case the flow rate of the stream, thesurface tension of the molten metal, and the size of the profile of therod should be such that substantially non-disruptive flow of the moltenmetal is obtained. Disturbed flow is desirable pursuant to the inventionbecause it promotes circulation within the confined stream and insuresuniform distribution of the treating agent throughout the host metal,but disruptive flow wherein the integrity of the stream is significantlyimpaired, as by breaking it up into smaller streams, is to be avoidedbecause it promotes dissolution of one or more components of the ambientatmosphere in the molten metal. The formation and maintenance of asingle coherent stream of molten metal from the pouring stage throughthe additive stage to the casting zone is thus made possible pursuant tothe practice of the invention. When the rod is fed obliquely into thestream but in the same general direction as the flow in the stream, themolten metal flows smoothly around the surface of the rod and the end ofthe rod that is eroded by melting resembles that of a melting icicle andfits smoothly into the flow of the metal. This latter arrangement willsupply the agent to the molten metal with a lesser degree of flowdisturbance than the other arrangements previously described butnevertheless do so with a sufficient degree of distribution andeffectiveness particularly when the length of the trough downstream ofthe point of entry of the rod is sufficient to make use of thedisturbance is flow created by the entering rod.

The rodlike master alloy can be readily fed to the molten host metalstream by the type of feed device used for supplying welding or brazingwire to a welding or brazing operation. The device advantageously iscapable of a variable feed rate so that the supply of master alloy tothe molten metal can be closely and accurately metered. If desired, thefeed device can also include a preheating element, such as an electricinduction coil surrounding the rodlike master alloy, close to its pointof introduction into the flowing stream of molten metal.

The following example is illustrative but not limitative of the practiceof the invention:

A %-inch diameter rod of the master alloy composed of 5 percent titaniumand 1 percent boron, both by weight, and the balance aluminum, was fedat the rate of inches of length per minute into a downwardly slopingcasting trough in the form of a single coherent stream of moltenaluminum flowing at the rate of 420 pounds per minute. The rod was fedobliqueten metal was supplied from a furnace at a temperature of about1,380 F., and the temperature of the molten aluminum at the point ofintroduction of the master alloy rod was about 1,300 F. The circulationof the molten metal at this temperature completely consumed the masteralloy rod as fast as it was, fed to the trough, and the disturbed butnonturbulent flow of the thus-inoculated molten metal, reflected by thewalls of the trough as it moved along the remainder of the trough to thecasting zone, produced a cast metal containing 0.002 percent by weightof titanium, as a grain refining agent in the form of titanium diborideand titanium-aluminum (TiAl thoroughly and uniformly distributedthroughout the resulting grain-refining aluminum casting.

It will be appreciated, accordingly, that the method of the presentinvention is particularly effective for inoculating molten metals andalloys with an alloying or grain refining agent in such manner that theagent is uniformly distributed throughout the molten metal by the timeit reaches the casting zone and remains similarly uniformly distributedthroughout the metal in the final casting. Although the method will findits maximum use in grain growth control and alloying operations, it canalso be used to introduce the same or other metals and intermetalliccompounds of various metals and elements into a molten metal so as toaid in cooling the metal in a direct chill casting operation and thusavoid cracking of the casting at high casting rates.

I claim:

1. The method of continuously introducing a metallic treating agent intoa molten metal which comprises pouring the molten metal from a sourcethereof into a confined troughlike passageway to form a stream of themolten metal flowing through the passageway, simultaneously feeding intothe stream of molten metal flowing in the passageway a solid rodlikesupply of the agent, the rodlike supply of the agent being introducedobliquely into the upstream portion of the stream of metal molten withthe end of the rod facing upstream into the flow of molten metal so asto effect a significant disturbance of the flow without impairing theintegrity of the stream and to permit the sidewalls of the trough toperpetuate said disturbance during flow of the molten metal throughoutthe remainder of the length of the trough in order to insure completemelting and assimilation of the treating agent in the molten metalstream, the rod being supplied at a rate not in excess of that at whichit is consumed in the flowing metal in the trough, and discharging theresulting molten metal into a casting zone.

2. The method of continuously introducing a metallic treating agent intoa molten metal which comprises pouring the molten metal from a sourcethereof into a confined troughlike passageway to form a stream of themolten metal flowing through the passageway, simultaneously feeding intothe stream of molten metal flowing in the passageway a solid rodlikesupply of the agent, the rodlike supply of the agent being introducedobliquely into the upstream portion of the stream of molten metal withthe end of the rod facing downstream into the flow of molten metal so asto effect a significant disturbance of the flow without impairing theintegrity of the stream and to permit the sidewalls of the trough toperpetuate said disturbance during flow of the molten metal throughoutthe remainder of the length of the trough in order to insure completemelting and assimilation of the treating agent in the molten metalstream, the rod being supplied at a rate not in excess of that at whichit is consumed in the flowing molten metal in the trough, anddischarging the resulting molten metal into a casting zone.

2. The method of continuously introducing a metallic treating agent intoa molten metal which comprises pouring the molten metal from a sourcethereof into a confined troughlike passageway to form a stream of themolten metal flowing through the passageway, simultaneously feeding intothe stream of molten metal flowing in the passageway a solid rodlikesupply of the agent, the rodlike supply of the agent being introducedobliquely into the upstream portion of the stream of molten metal withthe end of the rod facing downstream into the flow of molten metal so asto effect a significant disturbance of the flow without impairing theintegrity of the stream and to permit the sidewalls of the trough toperpetuate said disturbance during flow of the molten metal throughoutthe remainder of the length of the trough in order to insure completemelting and assimilation of the treating agent in the molten metalstream, the rod being supplied at a rate not in excess of that at whichit is consumed in the flowing molten metal in the trough, anddischarging the resulting molten metal into a casting zone.